Clustering of sleep electroencephalographic patterns in patients with the fibromyalgia (FM) syndrome

Several electroencephalographic (EEG) abnormalities have been
observed during sleep in patients suffering from the
fibromyalgia syndrome (FMS). In this study, 12 patients with
fibromyalgia and 14 control subjects had two polysomnographic
recordings obtained at home. Data from the second night were
subjected to blinded manual scoring as well as signal
processing using linked or 'step-wise clustering for pattern
recognition. In this procedure, a common learning set was
generated using the spectral information in three 2 min EEG
samples from each of the sleep stages selected from five
patients with FMS and five controls. In this way, 17
characteristic EEG classes were defined. All 2 s EEG segments
from the whole night from all subjects were then assigned to
one of these classes. Five of the classes (dominated by
0.5-4.5 Hz activity) were more frequent in the control group,
whereas three other classes (dominated by 8-11 Hz activity)
were prevalent in the patient group. This trend was consistent
in all sleep stages, although most striking in non-rapid eye
movement (NREM) sleep. The predominance of these classes in
the patient group may correspond to the alpha-EEG sleep
anomaly previously reported in subjects with FMS. More
importantly, as the EEG power in the lowest frequency range
(prevalent in controls) probably is a marker for restorative
sleep, the findings may reflect important aspects of sleep
disturbances n subjects suffering from FMS, thereby
contributing to some of the daytime symptoms in these
patients.